There are many electronic systems for which it is highly undesirable to permit tampering with the circuitry. For instance, any device relating to the security of financial transactions is vulnerable if the circuitry can be tampered with. A bank card reader, such as a point of sale device, for example, could thus be hacked or otherwise compromised to bypass the security and used for criminal purposes.
Many such devices have therefore been created which involve a security circuit; a circuit which is easily broken when tampered and which consequently permanently deactivates the device. Typically the security circuit will take the form of a flexible or deformable layer having conductive connections, typically formed as conductive tracks, on a lower surface which can be laid over a primary circuit. The conductive tracks can be actuated into electrical contact with the primary circuit, thereby completing the circuit. If the device is tampered with, the conductive tracks will be severed, destroying the security circuit, and breaking the connections of the primary circuit.
In the case of a bank card reader, there is a security circuit which covers switching domes. When a keypad button is depressed, the security circuit deforms collapsing the switching dome, shorting together switch contacts on the PCB, located under the centre of the dome and around the outer edge of the dome.
Similar security domes are provided to electrically connect the security circuit to the primary circuit. These domes are held in the operated condition by movable spigots associated with the housing, when the housing is in the closed condition. Opening of the housing moves at least one of these spigots, releasing the associate dome, thereby triggering an alarm condition. This allows a transaction to progress, safe in the knowledge that no third party has interfered with the reader.
In order to be able to effectively complete the security circuit, the keypad button or moveable spigot must be positioned at or adjacent the PCB. Such an arrangement may make it obvious to someone attempting to interfere with the reader as to where the PCB is located within the device, which may in fact aid tampering.
Additionally, such security domes use a dedicated biasing spring positioned between the primary circuit and the security circuit, and typically a plurality of such biasing springs at various positions within the housing or enclosure, which can cause a significant separation force to be imparted to the housing or enclosure. As such, the housing or enclosure has to be suitably formed and robust to prevent or limit the possibility of separation, cracking or splitting over time and during use. The limited available internal space to allow for reinforcement to meet the required robustness necessarily affects where such security devices can be placed within the housing or enclosure.